The present invention relates to a process for determining the roll angle in a launchable body, such as a rotary projectile, shell, missile, etc., which is launchable from a launcher, induced fields being used to establish the roll angle of the launchable body as it leaves the launcher by at least one inducing field being generated in the launcher and the inducing field or fields being detected in the launchable body. The invention also relates to a device for determining the roll angle in a launchable body, such as a rotary projectile, shell, missile, etc., which is launchable from a launching tube forming part of a launcher, which device comprises magnetic-field-generating members and magnetic-field-detecting members for establishing the roll angle of the launchable body when the body leaves the launching tube of the launcher, the magnetic-field-generating members being arranged in connection with the launching tube and the magnetic-field-detecting members being housed in the launchable body.
The invention is applicable to all types of projectiles, missiles, etc. which are launched from a firing tube or launching tube and which rotate in their trajectory. More specifically, the invention can be used with so-called final-phase-guided ammunition, i.e. projectiles which are conventionally fired in a ballistic trajectory to the immediate vicinity of the target where they receive a command for necessary correction. Because of the fact that the projectile rotates in its trajectory, its roll position has to be determined when the command is executed. In the absence of roll-position-determining members, an error otherwise occurs in the course correction.
A device for determining the roll angle in a launchable body is previously known by virtue of EP, A1, 0 319 649. An induced field is used to establish the roll angle of the launchable body as it leaves the launcher. The induced field is generated in the launcher and detected in the launchable body. At the moment of launch, the roll angle determined in the launchable body is considered to have acceptable precision. Since no monitoring is made of the rotational velocity of the rotatable body after the moment of launch, the rotatable body does however risk the imminent introduction of unacceptable deviation into the roll angle position.
Another device for determining roll angle is previously known by virtue of Swedish patent 465 794. In this case a permanent magnet is fitted in the launchable body, which, when the body is launched from the launching tube of the launcher, induces a field in windings fitted in the launching tube. The roll angle at the moment of launch is able to be determined through expedient signal processing. Information on this roll angle and the time which has elapsed since the launch is fed via a communications link to the launchable body which, with the aid of integrated electronics, calculates from this the rotation position in question. Assuming that the rotational velocity of the launchable body is able to be predicted or determined with high accuracy throughout the flight course of the body up to a possible point of correction, the known device offers the chance to calculate the rotation position with an accuracy which in normal cases is acceptable. If, however, the rotational velocity which is applied in calculating a roll angle position deviates from the correct rotational velocity, then the error in the roll angle position, especially when a long time has elapsed since the launch, will be unacceptable.
One object of the present invention is to achieve a process and a device which offer great accuracy without consequently entailing great complexity. Another object is to achieve simple communication between launcher and the launchable body.
The objects of the invention are achieved through a process characterized in that, for determination of the roll angle, communication is established between the launcher and the launchable body during the travel of the launchable body by the transmission of a polarized carrier wave in connection with the launcher and in that the transmitted polarized carrier wave is detected in the launchable body with regard to rotation dependency, and a device characterized in that a transmitter is arranged in connection with the launcher for communication with the launchable body by the transmission of a polarized carrier wave and in that the launchable body comprises a polarization-direction-sensitive receiver, the polarization-direction-sensitivity of which is arranged to track the rotation of the launchable body.
By housing the magnetic-field-detecting members in the launchable body, the launchable body is able independently to keep track of its roll angle on the basis of angular position at the moment of launch and counting of minima in a carrier-wave signal.
According to an advantageous process, the roll angle of the launchable body at the moment of launch is determined in the launchable body on the basis of the induced field or fields, minima are detected and counted in the transmitted polarized carrier wave from the point of launch and a time measurement is started at the moment of launch. By keeping track of minima and coupling these to the roll angle of the launchable body as it leaves the launcher, a simple solution is obtained to the problem of unambiguity in differentiating between 0 and xcfx80 radians.
According to a further advantageous process based on previous processes, for first detected minima it is established, starting from the roll angle determined at the moment of launch, whether the minimum corresponds to 0 or xcfx80 radians based on the field or fields induced at the moment of launch.
A specific angle of rotation xcex1 for the launchable body following the point in time tzero(n+1) is identified as the time t, in which
t=xcex1/360xc2x7T,
2xc2x7xcex94t=T,
xcex94t=tzero(n+1)xe2x88x92tzero(n)
and
tzero(n) represents the point in time following the launch moment when the nth. minimum in the polarized carrier wave is detected.
Advantageously, the magnetic-field-generating members are constituted by a first and a second permanent magnet arranged on the launching tube and mutually rotated 90 degrees relative to the axis of symmetry of the launching tube in order each to generate a magnetic field in respectively a first and second radial direction through the tube, which directions are rotated 90 degrees.
In order to detect the generated magnetic field, the launchable body is advantageously provided with magnetic-field-detecting members comprising a coil and a first and a second sample and holding circuit, the output signal levels of which are fed to a processor.
Advantageously, the launchable body comprises further minima-detecting means in the signal which the launchable body receives from the transmitter arranged in connection with the launcher and means for counting detected minima.
According to an advantageous embodiment, the minima-detecting means comprises a phase detector and a processor. The means for counting detected minima is expediently constituted by a processor.
According to another advantageous embodiment, the launchable body in the device according to the invention comprises time-measuring means. In a device according to the invention in which the launchable body is provided with one or more control charges, the time-measuring means herein defines the simultaneous triggering time of one or more control charges on the basis of transmitted angle information a and detected minima.